Device to-device communications apparatus and methods

ABSTRACT

As a result of the selection/reselection operation, a wireless terminal ( 26 ) selects the high priority candidate frequency for use in the device-to-device (D2D) communications. During the cell selection/reselection operation, the wireless terminal ( 26 ) is required to consider selection/reselection candidate frequencies at which the wireless terminal ( 26 ) cannot receive or transmit device-to-device (D2D) signals to be of low priority candidate frequencies when the wireless terminal ( 26 ) is capable of device-to-device (D2D) communications and is receiving or transmitting, or anticipating receiving or transmitting, device-to-device (D2D) signals on device-to-device (D2D) supported frequencies. In another basic mode predefined RRC Idle Mode state transition(s) are used to determine when a wireless terminal ( 26 ) encounters an out-of-coverage situation for device-to-device (D2D) communications purposes; and when the out-of-coverage situation is determined, the wireless terminal ( 26 ) uses pre-configured device-to-device (D2D) radio resources for the device-to-device (D2D) communications.

This application claims the priority and benefit of the following UnitedStates Provisional Patent application, which is incorporated herein byreference: U.S. Provisional Patent application 61/955,010 filed Mar. 18,2014, entitled “DETECTING OUT-OF-COVERAGE TRANSITION FOR WIRELESSDEVICE-TO-DEVICE COMMUNICATIONS”.

TECHNICAL FIELD

The technology relates to wireless communications, and particularly toallocating or granting radio resources for wireless device-to-device(D2D) communications.

BACKGROUND

When two user equipment terminals (e.g., mobile communication devices)of a cellular network or other telecommunication system communicate witheach other, their data path typically goes through the operator network.The data path through the network may include base stations and/orgateways. If the devices are in close proximity with each other, theirdata path may be routed locally through a local base station. Ingeneral, communications between a network node such as a base stationand a wireless terminal is known as “WAN” or “Cellular communication”.

It is also possible for two user equipment terminals in close proximityto each other to establish a direct link without the need to go througha base station. Telecommunications systems may use or enabledevice-to-device (“D2D”) communication, in which two or more userequipment terminals directly communicate with one another. In D2Dcommunication, voice and data traffic (referred to herein as“communication signals”) from one user equipment terminal to one or moreother user equipment terminals may not be communicated through a basestation or other network control device of a telecommunication system.Device-to-device (D2D) communication has more recently also become knownas “sidelink direct communication”.

D2D communication, e.g., sidelink direct communication, can be used innetworks implemented according to any suitable telecommunicationsstandard. A non-limiting example of such as standard is the 3rdGeneration Partnership Project (“3GPP”) Long Term Evolution (“LTE”). The3GPP standard is a collaboration agreement that aims to define globallyapplicable technical specifications and technical reports for third andfourth generation wireless communication systems. The 3GPP may definespecifications for next generation mobile networks, systems, anddevices. The 3GPP LTE is the name given to a project to improve theUniversal Mobile Telecommunications System (“UMTS”) mobile phone ordevice standard to cope with future requirements. In one aspect, UMTShas been modified to provide support and specification for the EvolvedUniversal Terrestrial Radio Access (“E-UTRA”) and Evolved UniversalTerrestrial Radio Access Network (“E-UTRAN”). E-UTRAN is anothernon-limiting example of a telecommunications standard with which D2Dcommunication may be used. A non-exhaustive list of 3GPP documents whichdescribe, at least in part, device-to-device (D2D) communication (e.g.,“sidelink direct communication”) include the following (all of which areincorporated herein by reference in their entireties):

3GPP TS 36.201 v12.1.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); LTE Physical Layer;General Description (Release 12) (2014 December);

3GPP TS 36.211 v12.4.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channelsand Modulation (Release 12) (2014 December);

3GPP TS 36.212 v12.3.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing andChannel Coding (Release 12) (2014 December);

3GPP TS 36.213 v12.0.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical LayerProcedures (Release 12) (2013 December);

3GPP TS 36.214 v12.1.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer;Measurements (Release 12) (2014 December);

3GPP TS 36.300 v12.4.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA) and EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN); OverallDescription; State 2 (Release 12) (2014 December);

3GPP TS 36.304 v12.3.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)Procedures in Idle Mode (Release 12) (2014 December);

3GPP TS 36.306 v12.3.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)Radio Access Capabilities (Release 12) (2014 December);

3GPP TS 36.321 v12.4.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Medium AccessControl (MAC) Protocol Specification (Release 12) (2014 December);

3GPP TS 36.322 v12.1.0, Technical Specification, 3rd GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control(RLC) Protocol Specification (Release 12) (2014 September);

3GPP TS 36.323 v12.2.0, Technical Specification, 3^(rd) GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Packet dataConvergence Protocol (PDCP) Specification (Release 12) (2014 December);and

3GPP TS 36.331 v12.4.0, Technical Specification, 3rd GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Radio ResourceControl (RRC) Protocol Specification (Release 12) (2014 December).

Device to device (D2D) communications provide proximity-basedapplications and services, representing an emerging social-technologicaltrend. The introduction of a Proximity Services (ProSe) capability inLTE allows the 3GPP industry to serve this developing market, and, atthe same time, serve the urgent needs of several Public Safetycommunities that are jointly committed to LTE. The current assumptionsrelated to D2D communication is that a wireless terminal within networkcoverage uses resources for D2D discovery and communication assigned bythe controlling node. If the wireless terminal is out of networkcoverage, it may use pre-assigned resources for communications. If thewireless terminal incorrectly determines its situation of in/out ofnetwork coverage, e.g., if the wireless terminal tries to use thepre-assigned resources within network coverage, it may affect thecurrent LTE networks with strong interference and thereby be verydangerous. Therefore, a problem which needs to be solved for D2Dcommunications is how the wireless terminal determines whether it is inor out of network coverage.

D2D services include ProSe Direct Communication (e.g., D2Dcommunication, sidelink direct communication) and ProSe Direct Discovery(e.g., D2D discovery, sidelink direct discovery). ProSe DirectCommunication is a mode of communication whereby two wireless terminalscan communicate with each other directly over the PC5 interface (i.e.,direct interface between two wireless terminals). This communicationmode is supported when the wireless terminal is served by E-UTRAN andwhen the wireless terminal is outside of E-UTRA coverage. A transmitterwireless terminal transmits a Scheduling assignment (SA) to indicate theresources it is going to use for data transmission to the receiverwireless terminals. ProSe Direct Discovery is defined as the procedureused by the ProSe-enabled wireless terminal to discover otherProSe-enabled wireless terminal(s) in its proximity using E-UTRA directradio signals via the PC5 interface.

Generally, the network coverage detection should be based on thedownlink received power. In current 3GPP specification TS 36.213,Version 12.0.0, see http://www.3gpp.org/DynaReport/36213.htm, thedownlink received power is measured with respect to cell-specificreference signal strength. The coverage can be defined by wirelessterminal's downlink received power measurement, or be defined bywireless terminal's RRC state for simpler implementation andspecification work. The downlink radio link quality of the primary cellis monitored by the wireless terminal for the purpose of indicatingout-of-sync/in-sync status to higher layers. The physical layer in thewireless terminal shall, in radio frames where the radio link quality isassessed, indicate out-of-sync to higher layers through a radio linkfailure (RLF) report when the radio link quality is worse than thethreshold Qout. When the radio link quality is better than the thresholdQin, the physical layer in the wireless terminal shall, in radio frameswhere the radio link quality is assessed, indicate in-sync to higherlayers.

Reusing the out-of-sync definition for out-of-coverage detection inrelation to D2D communication has several problems. For example, the RLFis only declared when the UE wireless terminal in RRC_CONNECTED mode.Furthermore, even the RLF is reported to be a correct out-of-coverageindication, it is for the primary cell only, i.e., the wireless terminalmay still be in coverage of other usable networks in the same area.

A wireless terminal in Long Term Evolution (LTE) may be in one of twoLTE radio resource control (RRC) states or modes: RRC_IDLE orRRC_CONNECTED. A wireless terminal is in RRC_CONNECTED when an RRCconnection has been established. If this is not the case (i.e., if noRRC connection is established) the wireless terminal is in RRC_IDLEstate. For RRC Idle mode wireless terminal, some metrics, such as thesynchronization signal (SS) strength or broadcast signal strength, maybe defined as measurement of out-of-coverage. However, these metrics arevery complicated to be implemented in LTE networks. All of these bringnew heavy burdens to legacy LTE networks.

For reasons mentioned above, in D2D communications when the D2D serviceand LTE cellular service share the same frequency band, the wirelessterminal needs to behave correctly based on whether it is in or outsidethe coverage of network, so as to minimize its compact (interference) onthe present networks, e.g., LTE networks. A problem in this area is todetect the network coverage accurately and efficiently, so that (amongother reasons) the wireless terminal in device-to-device (D2D)communications will not interfere with network operation.

What is needed, therefore, among other things are methods, apparatus,and/or techniques for selecting resource utilization methods forpurposes such as controlling behavior of a device-to-device (D2D)capable wireless terminal and detecting network coverage for purposessuch as ascertaining whether a device-to-device (D2D) capable wirelessterminal is in-coverage or out-of-coverage, such as (for example) whenthe wireless terminal is in Idle Mode. The methods, apparatus, and/ortechniques provide benefits that reduce system complexity and improvecommunication flexibility and efficiency.

In D2D communications, if the D2D service and LTE cellular service sharethe same frequency, the resource allocation to UE needs to be performedcorrectly based on whether it is in or outside the coverage of network,so as to minimize its compact (interference) on the present networks,e.g., LTE networks. On the other hand, the issue of load balancing mayalso be pertinent for an in coverage scenario when one resourceallocation method cannot have adequate resources for allocation whileanother method still has enough resources.

SUMMARY

In one of its aspects the technology disclosed herein concerns a methodin a wireless terminal which is in wireless communications with a radioaccess node over a radio interface. In a basic embodiment and mode themethod comprises, when the wireless terminal is configured to performdevice-to-device (D2D) communications while camping on a frequency,during a cell selection/reselection operation the wireless terminalconsidering the camped-on frequency to be a high priority candidatefrequency.

In an example embodiment and mode the method further comprises, as aresult of the selection/reselection operation the wireless terminalselecting a candidate frequency for use in the device-to-device (D2D)communications.

In an example embodiment and mode the method further comprises, as aresult of the selection/reselection operation, the wireless terminalselecting the high priority candidate frequency for use in thedevice-to-device (D2D) communications.

In an example embodiment and mode the method further comprises, duringthe cell selection/reselection operation, requiring the wirelessterminal to consider selection/reselection candidate frequencies atwhich the wireless terminal cannot receive or transmit device-to-device(D2D) signals to be of low priority candidate frequencies when thewireless terminal is capable of device-to-device (D2D) communicationsand is receiving or transmitting, or anticipating receiving ortransmitting, device-to-device (D2D) signals on device-to-device (D2D)supported frequencies.

In an example embodiment and mode the method further comprises duringthe cell selection/reselection operation, requiring the wirelessterminal to consider only cell selection/reselection candidatefrequencies which are device-to-device (D2D)-supported frequencies whenthe wireless terminal is capable of device-to-device (D2D)communications and is receiving or transmitting, or anticipatingreceiving or transmitting, the device-to-device (D2D) signals on thedevice-to-device (D2D) supported frequencies.

In an example embodiment and mode the method further comprises:determining whether the wireless terminal when engaged indevice-to-device (D2D) communications encounters a wireless terminalselected resource mode; and the wireless terminal determining whether totransmit the device-to-device (D2D) signals using resources selected bythe wireless terminal from pre-configured device-to-device (D2D) radioresources or using network-allocated radio resources scheduled by thenode based on determining whether the wireless terminal encounters thewireless terminal selected resource mode.

In an example embodiment and mode the method further comprises thewireless terminal transmitting device-to-device (D2D) signals usingdevice-to-device (D2D) radio resources selected in accordance with thecell selection/reselection operation.

In another of its aspects the technology disclosed herein concerns awireless terminal of a communications network which communicates over aradio interface with a radio access node. The wireless terminalcomprises a processor which is configured, during a cellselection/reselection operation when the wireless terminal is performingthe device-to-device (D2D) communications while camping on frequency, toconsider the camped-on frequency to be a high priority candidatefrequency for the cell selection/reselection operation.

In an example embodiment, as a result of the selection/reselectionoperation, the processor is configured to select a candidate frequencyfor use in the device-to-device (D2D) communications.

In an example embodiment, as the result of the selection/reselectionoperation, the processor is configured to select the high prioritycandidate frequency for use in the device-to-device (D2D)communications.

In an example embodiment the processor is configured to require, duringthe cell selection/reselection operation, the wireless terminal toconsider selection/reselection candidate frequencies at which thewireless terminal cannot receive or transmit device-to-device (D2D)signals to be of low priority candidate frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

In an example embodiment the processor is configured to require, duringa cell selection/reselection operation, the wireless terminal toconsider only cell selection/reselection candidate frequencies which aredevice-to-device (D2D)-supported frequencies when the wireless terminalis capable of device-to-device (D2D) communications and is receiving ortransmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

In an example embodiment the wireless terminal further comprises atransceiver configured to transmit device-to-device (D2D) signals usingdevice-to-device (D2D) radio resources selected in accordance with thecell selection/reselection operation.

In another of its aspects the technology disclosed herein concerns amethod in a wireless terminal which is in wireless communications with aradio access node over a radio interface. In a basic mode the methodcomprises using a predefined RRC Idle Mode state transition to determinewhen a wireless terminal encounters an out-of-coverage situation fordevice-to-device (D2D) communications purposes; and when theout-of-coverage situation is determined, the wireless terminal usingpre-configured device-to-device (D2D) radio resources for thedevice-to-device (D2D) communications.

In an example embodiment and mode the method further comprises thewireless terminal transmitting device-to-device (D2D) signals to anotherwireless terminal using the pre-configured device-to-device (D2D) radioresources.

In an example embodiment and mode the predefined RRC Idle Mode statetransition comprises any one of the following:

-   -   (1) the wireless terminal moving to Any Cell Selection State;    -   (2) the wireless terminal moving to Camped Normally State on        non-device-to-device (D2D) frequencies;    -   (3) the wireless terminal moving to Camped on Any Cell State on        non-device-to-device (D2D) frequencies.

In an example embodiment and mode the method further comprises: when thewireless terminal undergoes any one of a set of predefined RRC Idle Modestate transitions, starting an out-of-coverage counter provided that theout-of-coverage counter is not already running and is not alreadyexpired; and upon expiration of the out-of-coverage counter, thewireless terminal transmitting the device-to-device (D2D) signals usingthe pre-configured device-to-device (D2D) radio resources.

In an example embodiment and mode the out-of-coverage counter is a clockwhich counts elapsing time units.

In an example embodiment and mode the out-of-coverage counter isconfigured to count occurrences of detection of a network event ormarker.

In an example embodiment and mode the method further comprises, when thecounter expires, the wireless terminal declaring itself out-of-coverageand transmitting the device-to-device (D2D) signals using thepre-configured radio resources.

In an example embodiment and mode the method further comprises, when thecounter expires, allowing the wireless terminal to transmit thedevice-to-device (D2D) signals using the pre-configured device-to-device(D2D) radio resources.

In an example embodiment and mode the method further comprises at leasttemporarily stopping the counter if any one of the following occurs:

-   -   the wireless terminal finds a suitable/acceptable cell to camp        on in device-to-device (D2D) supported frequencies;    -   the wireless terminal is no longer participating in        device-to-device (D2D) services/communications;    -   the wireless terminal determines that the wireless terminal is        out-of-coverage;    -   the wireless terminal leaves the Idle Mode.

In an example embodiment and mode the method further comprises, during acell selection/reselection operation, permitting the wireless terminalto consider only cell selection/reselection candidate frequencies whichare device-to-device (D2D)-supported frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

In an example embodiment and mode the method further comprises, during acell selection/reselection operation, requiring the wireless terminal toconsider selection/reselection candidate frequencies at which thewireless terminal cannot receive or transmit device-to-device (D2D)signals to be of low priority candidate frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

In another of its aspects the technology disclosed herein concerns awireless terminal which is in wireless communications with a radioaccess node over a radio interface. In a basic example embodiment thewireless terminal comprises a processor configured to use a predefinedRRC Idle Mode state transition to determine when a wireless terminalencounters an out-of-coverage situation for device-to-device (D2D)communications purposes; and when the out-of-coverage situation isdetermined, to use pre-configured device-to-device (D2D) radio resourcesfor the device-to-device (D2D) communications.

In an example embodiment the wireless terminal further comprises atransmitter configured to send device-to-device (D2D) signals to anotherwireless terminal using the pre-configured device-to-device (D2D) radioresources.

In an example embodiment the predefined RRC Idle Mode state transitioncomprises any one of the following:

-   -   (1) the wireless terminal moving to Any Cell Selection State;    -   (2) the wireless terminal moving to Camped Normally State on        non-device-to-device (D2D) frequencies;    -   (3) the wireless terminal moving to Camped on Any Cell State on        non-device-to-device (D2D) frequencies.

In an example embodiment the processor is further configured: when thewireless terminal undergoes any one of a set of predefined RRC Idle Modestate transitions, to start an out-of-coverage counter provided that theout-of-coverage counter is not already running and is not alreadyexpired; and upon expiration of the out-of-coverage counter, to transmitthe device-to-device (D2D) signals using the pre-configureddevice-to-device (D2D) radio resources.

In an example embodiment the out-of-coverage counter is a clock whichcounts elapsing time units.

In an example embodiment the out-of-coverage counter is configured tocount occurrences of detection of a network event or marker.

In an example embodiment the processor is further configured, when thecounter expires, to declare the wireless terminal out-of-coverage and totransmit the device-to-device (D2D) signals using the pre-configuredradio resources.

In an example embodiment the processor is further configured, when thecounter expires, to allow the wireless terminal to transmit thedevice-to-device (D2D) signals using the pre-configured device-to-device(D2D) radio resources

In an example embodiment the processor is further configured to at leasttemporarily stop the counter if any one of the following occurs:

-   -   the wireless terminal finds a suitable/acceptable cell to camp        on in device-to-device (D2D) supported frequencies;    -   the wireless terminal is no longer participating in        device-to-device (D2D) services/communications;    -   the wireless terminal determines that the wireless terminal is        out-of-coverage;    -   the wireless terminal leaves the Idle Mode.

In an example embodiment the processor is further configured, during acell selection/reselection operation, to permit the wireless terminal toconsider only cell selection/reselection candidate frequencies which aredevice-to-device (D2D)-supported frequencies when the wireless terminalis capable of device-to-device (D2D) communications and is receiving ortransmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

In an example embodiment the processor is further configured, during acell selection/reselection operation, to require the wireless terminalto consider selection/reselection candidate frequencies at which thewireless terminal cannot receive or transmit device-to-device (D2D)signals to be of low priority candidate frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of thetechnology disclosed herein will be apparent from the following moreparticular description of preferred embodiments as illustrated in theaccompanying drawings in which reference characters refer to the sameparts throughout the various views. The drawings are not necessarily toscale, emphasis instead being placed upon illustrating the principles ofthe technology disclosed herein.

FIG. 1A-FIG. 1C are schematic views of example embodiments of radiocommunications networks in which a wireless terminal participate indevice-to-device (D2D) communications and implement respective aspectsof the technology disclosed herein.

FIG. 2 is a diagrammatic view depicting different types of cellselection/re-selection strategies which may be utilized in conjunctionwith example out-of-coverage detection methods.

FIG. 3A is a flowchart depicting basic, example acts or steps involvedin a generic method of determining when a wireless terminal engaged indevice-to-device (D2D) communications encounters an out-of-coveragesituation.

FIG. 3B is a flowchart depicting basic, example acts or steps involvedin a counter-based method of determining when a wireless terminalengaged in device-to-device (D2D) communications encounters anout-of-coverage situation.

FIG. 4 is a schematic view of a more detailed example implementationwhich may be implemented for any or all of the embodiments of FIG.1A-FIG. 1C.

FIG. 5 is a schematic view illustrating an example embodiment ofelectronic machinery that may comprise a radio access node and/or awireless terminal.

FIG. 6 shows transitions and logic of RRC Idle.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the technology disclosed herein. However, itwill be apparent to those skilled in the art that the technologydisclosed herein may be practiced in other embodiments that depart fromthese specific details. That is, those skilled in the art will be ableto devise various arrangements which, although not explicitly describedor shown herein, embody the principles of the technology disclosedherein and are included within its spirit and scope. In some instances,detailed descriptions of well-known devices, circuits, and methods areomitted so as not to obscure the description of the technology disclosedherein with unnecessary detail. All statements herein recitingprinciples, aspects, and embodiments of the technology disclosed herein,as well as specific examples thereof, are intended to encompass bothstructural and functional equivalents thereof. Additionally, it isintended that such equivalents include both currently known equivalentsas well as equivalents developed in the future, i.e., any elementsdeveloped that perform the same function, regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat block diagrams herein can represent conceptual views ofillustrative circuitry or other functional units embodying theprinciples of the technology. Similarly, it will be appreciated that anyflow charts, state transition diagrams, pseudocode, and the likerepresent various processes which may be substantially represented incomputer readable medium and so executed by a computer or processor,whether or not such computer or processor is explicitly shown.

As used herein, the term “device-to-device (“D2D”) communication” canrefer to a mode of communication between or among wireless terminalsthat operate on a cellular network or other telecommunications system inwhich the communication data traffic from one wireless terminal toanother wireless terminal does not pass through a centralized basestation or other device in the cellular network or othertelecommunications system. As explained above, device-to-device (D2D)communication is also known by the more recent term “sidelink directcommunication”. Communication data is sent using communication signalsand can include voice communications or data communications intended forconsumption by a user of a wireless terminal Communication signals maybe transmitted directly from a first wireless terminal to a secondwireless terminal via D2D communication. In various aspects, all, someor none of the control signaling related to the D2D packet transmissionmay be managed or generated by the underlying core network or basestation. In additional or alternative aspects, a receiver user equipmentterminal may relay communication data traffic between a transmitter userequipment terminal and one or more additional receiver user equipmentterminals.

As used herein, the term “core network” can refer to a device, group ofdevices, or sub-system in a telecommunication network that providesservices to users of the telecommunications network. Examples ofservices provided by a core network include aggregation, authentication,call switching, service invocation, gateways to other networks, etc.

As used herein, the term “wireless terminal” can refer to any electronicdevice used to communicate voice and/or data via a telecommunicationssystem, such as (but not limited to) a cellular network. Otherterminology used to refer to wireless terminals and non-limitingexamples of such devices can include user equipment terminal, UE, mobilestation, mobile device, access terminal, subscriber station, mobileterminal, remote station, user terminal, terminal, subscriber unit,cellular phones, smart phones, personal digital assistants (“PDAs”),laptop computers, netbooks, e-readers, wireless modems, etc.

As used herein, the term “access node”, “node”, or “base station” canrefer to any device or group of devices that facilitates wirelesscommunication or otherwise provides an interface between a wirelessterminal and a telecommunications system. A non-limiting example of abase station can include, in the 3GPP specification, a Node B (“NB”), anenhanced Node B (“eNB”), a home eNB (“HeNB”) or some other similarterminology. Another non-limiting example of a base station is an accesspoint. An access point may be an electronic device that provides accessfor wireless terminal to a data network, such as (but not limited to) aLocal Area Network (“LAN”), Wide Area Network (“WAN”), the Internet,etc. Although some examples of the systems and methods disclosed hereinmay be described in relation to given standards (e.g., 3GPP Releases 8,9, 10, 11, and/or 12), the scope of the present disclosure should not belimited in this regard. At least some aspects of the systems and methodsdisclosed herein may be utilized in other types of wirelesscommunication systems.

As used herein, the term “telecommunication system” or “communicationssystem” can refer to any network of devices used to transmitinformation. A non-limiting example of a telecommunication system is acellular network or other wireless communication system.

As used herein, the term “cellular network” can refer to a networkdistributed over cells, each cell served by at least one fixed-locationtransceiver, such as a base station. A “cell” may be any communicationchannel that is specified by standardization or regulatory bodies to beused for International Mobile Telecommunications-Advanced(“IMTAdvanced”). All or a subset of the cell may be adopted by 3GPP aslicensed bands (e.g., frequency band) to be used for communicationbetween a base station, such as a Node B, and a UE terminal. A cellularnetwork using licensed frequency bands can include configured cells.Configured cells can include cells of which a UE terminal is aware andin which it is allowed by a base station to transmit or receiveinformation.

As used herein, a “D2D signal” or “D2D signals” include channels,reference signals, and synchronization signals for D2D communicationand/or discovery.

One of the aspects of the technology disclosed herein provides, e.g.,solutions for detecting LTE network coverage for the purpose of D2Dcommunications. Prevailing current consensus is that network coveragedetection should be at least based on the downlink received power.However, the technology disclosed herein, rather than requiring any newtype of received signal power measurement and/or new processing, takesadvantage of and capitalizes upon the already known wireless terminalstate information, especially the idle mode UE states, for networkcoverage detection.

As a prelude to discussion of the out-of-coverage detection methods andapparatus of the technology disclosed herein, brief general overviewsare provided of the Idle Mode; of cell classifications and service typesfor the RRC Idle state, and of basic concepts of cell selection andre-selection.

If a wireless terminal is in RRC_CONNECTED mode, there is normal RRCconnection between wireless terminal and the radio access node (e.g.,eNodeB), so the wireless terminal is obviously in the network coverage.But when the wireless terminal is in the Idle Mode the wireless terminalmay or may not be in network coverage (e.g., in-coverage). TS 36.304 (V11.6.0) lists five radio resource control (RRC) states for a wirelessterminal, three of which pertain to Idle Mode. The three RRC stateswhich pertain to Idle Mode are: “Camped Normally”, “Camped on Any Cell”;and “Any Cell Selection”.

In the Camped Normally state the wireless terminal selects and monitorsthe indicated Paging Channels of the cell according to information sentin system information; monitors relevant System Information (SI);performs necessary measurements for the cell reselection evaluationprocedure; and executes the cell reselection evaluation process uponoccurrence of certain occasions/triggers.

In the Camped on Any Cell state the wireless terminal monitors relevantSystem Information; performs necessary measurements for the cellreselection evaluation procedure; and executes the cell reselectionevaluation process upon occurrence of certain occasions/triggers. Inaddition, the wireless terminal regularly attempts to find a suitablecell by trying all frequencies of all radio access technologies (RATs)that are supported by the wireless terminal. If a suitable cell isfound, the wireless terminal moves to Camped Normally state. If thewireless terminal supports voice services and the current cell does notsupport emergency call as indicated in System Information, the wirelessterminal performs cell selection/reselection to an acceptable cell ofany supported RAT regardless of priorities provided in systeminformation from current cell, if no suitable cell is found.

In the Any Cell Selection state the wireless terminal attempts to findan acceptable cell of any public land mobile network (PLMN) to camp on,trying all radio access technologies (RATs) that are supported by thewireless terminal and searching first for a high quality cell.

The action of camping on a cell is necessary to get access to someservices. In general, there are three levels of services defined for awireless terminal. The first service level, limited service, allowsemergency calls, Earthquake and Tsunami Warning System (ETWS), andCommercial Mobile Alert System (CMAS) on an acceptable cell. The secondservice level, normal service, enables public use on a suitable cell.The third service level, operator service, is for operators only on areserved cell.

As apparent from the foregoing, cells are categorized according to whatservices they offer. Mentioned above are “suitable cell”, “reservedcell”, and “acceptable cell”. An “acceptable cell” is a cell on whichthe wireless terminal may camp to obtain limited service (originateemergency calls and receive ETWS and CMAS notifications). Such a cellfulfills a minimum set of requirements to initiate an emergency call andto receive ETWS and CMAS notification in an E-UTRAN network. A “suitablecell” is a cell on which the wireless terminal may camp on to obtainnormal service. The UE shall have a valid USIM and such a cell shallfulfill certain specified requirements. A cell is a “reserved cell” ifit is indicated as reserved in system information.

On request of a Non-Access Stratum (NAS) a search is performed foravailable PLMNs. In so doing, the wireless terminal scans all radiofrequency (RF) channels in the E-UTRA bands according to itscapabilities to find available PLMNs. On each carrier the wirelessterminal searches for the strongest cell and reads its systeminformation, in order to find out to which PLMN(s) the cell belongs. Ifthe wireless terminal can read one or several PLMN identities in thestrongest cell, each found PLMN is reported to the NAS as a high qualityPLMN (but without the RSRP value), provided that the certain qualitycriterion is fulfilled. Found PLMNs that do not satisfy the high qualitycriterion, but for which the wireless terminal has been able to read thePLMN identities, are reported to the NAS together with the RSRP value.Once the wireless terminal has selected a PLMN, the cell selectionprocedure is performed in order to select a suitable cell of that PLMNto camp on.

In a cell selection and re-selection procedure the wireless terminalperforms certain specified measurements. The NAS can control the RAT(s)in which the cell selection is performed, for instance by indicatingRAT(s) associated with the selected PLMN, and by maintaining a list offorbidden registration area(s) and a list of equivalent PLMNs. Thewireless terminal selects a suitable cell based on idle modemeasurements and cell selection criteria. When camped on a cell, thewireless terminal regularly searches for a better cell according to thecell reselection criteria. If a better cell is found, that cell isselected. The change of cell may imply a change of RAT.

Thus, the wireless terminal may transition through the three previouslymentioned states in conjunction with the Idle Mode. Through cellselection/reselection, a wireless terminal in Idle Mode moves to CampedNormally state if the wireless terminal finds a suitable cell (selectedPLMN is available) to camp on without registration rejection. Otherwise,the wireless terminal moves to Any Cell Selection state. The wirelessterminal moves to Camped on Any Cell state if the wireless terminalfinds an acceptable cell (selected PLMN is unavailable) to camp on. Ifno acceptable cell is found, the wireless terminal stays in Any CellSelection state. If the wireless terminal in Camped on Any Cell statefinds a suitable cell to camp on, the wireless terminal moves to “CampedNormally” directly. These transitions, among other aspects of Idle Mode,are illustrated in FIG. 6, which is reproduced from 3GPP TS 36.304V8.2.0 (2008 May) section 5.2.2., incorporated herein by reference inits entirety.

A. Network, Node, and Device Overview

FIG. 1A shows an example communications system 20 wherein radio accessnode 22 communicates over air or radio interface 24 with first wirelessterminal 26 ₁. The node 22 comprises node processor 30 and nodetransmitter 32. The first wireless terminal 26 ₁ comprises terminalprocessor 40 and terminal transceiver 42. The terminal transceiver 42typically comprises terminal transmitter circuitry 44 and terminalreceiver circuitry 46.

In general operation node 22 and first wireless terminal 26 ₁communicate with each other across radio interface 24, and may do sousing “frames” of information that are typically formatted and preparedby a scheduler of node 22. In Long Term Evolution (LTE) a frame, whichmay have both downlink portion(s) and uplink portion(s), is communicatedbetween the node and the wireless terminal Each LTE frame may compriseplural subframes. In the time domain, each LTE subframe may be dividedinto two slots. The transmitted signal in each slot is described by aresource grid comprised of resource elements (RE).

Long Term Evolution (LTE) defines a number of downlink physical channelswhich carry information received from Medium Access Control (MAC) andhigher layers. In Long Term Evolution (LTE) no dedicated data channelsare used, instead shared channel resources are used in both downlink anduplink. For example, the Physical Downlink Shared Channel (PDSCH) is themain physical channel used for unicast data transmission, and is alsoused for transmission of paging information. These shared resources arecontrolled by one or more schedulers that assign(s) different parts ofthe downlink and uplink shared channels to different wireless terminalsfor reception and transmission respectively. The assignments for theshared channels are transmitted in a control region which is provided inthe beginning of each downlink subframe. The Physical Downlink ControlChannel (PDCCH) carries the resource assignment for wireless terminals.

When a wireless terminal desires to send information on the uplink tothe node 22, the wireless terminal sends a scheduling request to thenode 22 followed by a buffer status report (BSR) from which the node 22can determine that the wireless terminal intends to perform an uplinktransmission. Thereafter in a downlink (DL) subframe the node 22indicates on the Physical Downlink Control Channel (PDCCH) what radioresources the wireless terminal may use for its desired uplinktransmission, e.g., the node 22 provides an uplink grant for an uplinktransmission.

As mentioned above, in some instances wireless terminals may communicatewith one another without having those communications transmitted throughthe node 22. Such terminal-to-terminal communications are also calleddevice-to-device (D2D) communications. At some times thedevice-to-device (D2D) communications may be under network control or“in-coverage”, meaning that one or more of the wireless terminalinvolved in the device-to-device (D2D) communications may be withinrange of radio frequencies utilized by a node or cell of a radio accessnetwork (RAN). When “in-coverage” care must be taken that use of radioresources of the device-to-device (D2D) communications not causeinterference with the other types of communications on-going in thecell, e.g., communications between the node 22 and the wirelessterminals served by the node 22.

The terminal transceiver 42 preferably comprises terminal transmittercircuitry (“transmitter”) 44 and terminal receiver circuitry(“receiver”) 46. The receiver 46 of first wireless terminal 26 ₁receives subframe S communicated over radio interface 24 fromcommunications system 20. When in-coverage, in conjunction withdevice-to-device (D2D) communications the terminal processor 40 mayobtain a device-to-device (D2D) grant from the subframe S. Thedevice-to-device (D2D) grant specifies radio resources that firstwireless terminal 26 ₁ is permitted to use for device-to-device (D2D)communication with another wireless terminal, e.g., second wirelessterminal 26 ₂. The transmitter 44 of first wireless terminal 26 ₁serves, e.g., to transmit data on the uplink (UL) from first wirelessterminal 26 ₁ to node 22, but may also serve to transmitdevice-to-device (D2D) data to another wireless terminal(s), e.g.,second wireless terminal 26 ₂, using the radio resources permitted bythe D2D grant.

There are two modes of device-to-device (D2D) resource allocation. Afirst mode has several names (all used interchangeably herein), such as“Mode 1”, the “eNB scheduled resource allocation mode”, and the“network-allocated resource mode”. Mode 1 is characterized by: (1) thewireless terminal needing to be RRC_CONNECTED in order to transmit data;(2) the wireless terminal requesting transmission resources from thenode (the node schedules transmission resources for transmission ofscheduling assignment(s) and data); (3) the wireless terminal sending ascheduling request (D-SR or Random Access) to the node followed by abuffer status report (BSR). Based on the BSR the node can determine thatthe wireless terminal has data for a ProSe Direct Communicationtransmission and estimate the resources needed for transmission.

A second mode also has several names (used interchangeably herein), suchas “Mode 2”, the “wireless terminal selected resource” mode (or, moresimply, the “terminal selected resource mode), and the “wirelessterminal (UE) autonomous resource selection mode”. Mode 2 ischaracterized by the wireless terminal (UE) on its own selectingresources from resource pools to transmit scheduling assignment anddata. The fact that a wireless terminal selects resources “on its own”indicates that the resource selection is “autonomous”.

One of the aspects of the technology disclosed herein provides, e.g.,techniques for determining when a wireless terminal such as wirelessterminal 26 ₁ is out-of-coverage. When out-of-coverage, the wirelessterminal 26 ₁ is no longer entitled for device-to-device (D2D)communications to use the network radio resources which are dynamicallyallocated by node 22. That is, when out-of-coverage the wirelessterminal may not use Mode 1. Instead, when out-of-coverage, the wirelessterminal 26 ₁ must use for device-to-device (D2D) communications (e.g.,communications with other wireless terminals such as second wirelessterminal 26 ₂) resources selected by the wireless terminal from apre-configured pool of radio resources (e.g., a wireless terminalselected resource mode). That is, when out-of-coverage the wirelessterminal uses Mode 2. FIG. 1A shows terminal processor 40 having accessto device-to-device (D2D) resource pool 48, which may at least partiallybe stored in memory for access by terminal processor 40.

FIG. 1A also shows the wireless terminal 26 ₁ as comprisingdevice-to-device (D2D) controller 50. The device-to-device (D2D)controller 50 performs functions for many embodiments and modesdescribed herein. The device-to-device (D2D) controller 50 and indeedwireless terminal 26 ₁ may comprise electronic machinery as describedherein with reference to FIG. 5, for example. Among the functionsperformed by device-to-device (D2D) controller 50 are (B) CellSelection/Re-Selection strategies; and (C) determining out-of-coveragesituations. While one or more of these functions may be performedtogether in a same example embodiment and mode, each function may alsobe separately performed without necessarily implementing or involvingaspects of other functions.

B. Cell Selection/Re-Selection Strategies

FIG. 1B shows that the device-to-device (D2D) controller 50 of wirelessterminal 26 ₁ may, in an embodiment and mode, comprise cellselection/re-selection logic 50B. FIG. 2 shows basic, example acts orsteps involved in a generic method of operating a wireless terminalengaged in device-to-device (D2D) communications, and particularlydifferent types of cell selection/re-selection strategies which may beutilized in conjunction with the example out-of-coverage detectionmethods. In an example embodiment and mode the acts of FIG. 2 may beperformed by cell selection/re-selection logic 50B of device-to-device(D2D) controller 50

One such cell selection/re-selection, represented by act 2-1 and knownas the D2D prioritized strategy, requires the wireless terminal toconsider selection/reselection candidate frequencies at which thewireless terminal cannot receive or transmit device-to-device (D2D)signals to be of low priority candidate frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies. It will be appreciated that, as just-stated, the wirelessterminal is receiving or transmitting, or anticipating receiving ortransmitting, device-to-device (D2D) signals on device-to-device (D2D)supported frequencies, and as a result of such actual or anticipatedreceiving or transmitting the wireless terminal is therefore “camped” ona particular frequency and is receiving the “camped on” frequenciesthrough its receiver circuit 46. As such, if the candidate frequenciesat which the wireless terminal cannot receive or transmitdevice-to-device (D2D) signals are considered in the D2D prioritizedstrategy of act 2-1 to be low priority candidate frequencies as juststated, then naturally the candidate frequencies at which the wirelessterminal can receive or transmit device-to-device (D2D) signals,including the camped-on frequency, are considered to be high prioritycandidate frequencies. Logically the already camped-on frequency will beconsidered to be the highest priority candidate frequency.

Another such cell selection/re-selection strategy, which is a refinementof the strategy of act 2-1, represented by act 2-2 and known as the D2Donly strategy, requires the wireless terminal (e.g., wireless terminal26 ₁) to consider only cell selection/reselection candidate frequencieswhich are device-to-device (D2D)-supported frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.

It will be appreciated that, as a result of the selection/reselectionoperation of either act 2-1 or act 2-1, the wireless terminal andparticularly terminal processor 40 selects a candidate frequency for usein the device-to-device (D2D) communications. For example, inconjunction with act 2-1 the terminal processor 40 may select a highpriority candidate as the candidate frequency for use in thedevice-to-device (D2D) communications.

In conjunction with the cell selection/re-selection strategy the atransceiver 42 is configured to transmit device-to-device (D2D) signalsusing device-to-device (D2D) radio resources selected in accordance withthe cell selection/reselection operation.

C. Determining Out-of-Coverage Situations

As mentioned above, one of the aspects of the technology disclosedherein provides techniques for determining when a wireless terminal suchas wireless terminal 26 ₁ is out-of-coverage. As shown in more detail inFIG. 1B terminal processor 40 comprises device-to-device (D2D)controller 50 with coverage detection logic 50C and radio resourcecontrol (RRC) state machine 52. As explained herein, in one aspect ofthe technology disclosed herein terminal processor 40 and particularlydevice-to-device (D2D) controller 50 thereof uses predefined RRC Idlestate transitions to determine when a wireless terminal engaged indevice-to-device (D2D) communications encounters an out-of-coveragesituation (e.g., a wireless terminal selected resource mode).

FIG. 3A shows basic, example acts or steps involved in a generic methodof determining when a wireless terminal encounters an out-of-coveragesituation for device-to-device (D2D) communications purposes.“Device-to-device (D2D) communication purposes” (and likewise sidelinkdirection communication purposes) may comprise a wireless terminalengaged in device-to-device (D2D) communications (e.g., alreadyparticipating in device-to-device (D2D) communications) or anticipatingparticipating in device-to-device (D2D) communications. The examplemethod of FIG. 3 may be used in conjunction with either the D2Dprioritized strategy of act 2-1 or the D2D only strategy of act 2-2. Act3A-1 comprises the terminal processor 40 using a predefined RRC Idlestate transition to determine when a wireless terminal engaged indevice-to-device (D2D) communications encounters an out-of-coveragesituation. Act 3A-2 comprises, when the out-of-coverage situation isdetermined, the terminal processor 40 transmitting (over terminaltransmitter circuitry 44) device-to-device (D2D) signals usingpre-configured resources. For example, act 3A-2 may comprise theterminal processor 40 causing the transmitter 44 of wireless terminal totransmit device-to-device (D2D) signals using resources selected by thewireless terminal from pre-configured device-to-device (D2D) radioresources. As understood from FIG. 1, the pre-configureddevice-to-device (D2D) resources may, in an example implementation, bethe resources of device-to-device (D2D) resource pool 48.

As used herein, the predefined RRC Idle state transition comprises anyone of the following: (1) the wireless terminal moving to Any CellSelection State; (2) the wireless terminal moving to Camped NormallyState on non-device-to-device (D2D) frequencies; (3) the wirelessterminal moving to Camped on Any Cell State on non-device-to-device(D2D) frequencies. Collectively these three transitions may be referredto as a set of RRC Idle state transitions, any one of which may indicatean out-of-coverage situation.

FIG. 3B shows basic, example acts or steps involved in a counter-basedmethod of determining when a wireless terminal engaged indevice-to-device (D2D) communications encounters an out-of-coveragesituation (e.g., a wireless terminal selected resource mode). Act 3B-1,which corresponds to an implementation of act 3A-1, comprises theterminal processor 40 starting a resource mode counter 60 (e.g., anout-of-coverage counter) when the wireless terminal undergoes any one ofthe set of predefined RRC Idle state transitions. FIG. 1C shows that, inan example embodiment and mode, device-to-device (D2D) controller 50 maycomprises a counter 60, known as the “out-of-coverage” counter oralternatively as the resource mode counter. In this regard, thedevice-to-device (D2D) controller 50 of terminal processor 40 requeststhat RRC state machine 52 notify the device-to-device (D2D) controller50 when any one of the set of predefined RRC Idle state transitionsoccurs, and such notification from RRC state machine 52 specifies thenature and/or circumstance of the RRC state transition. Act 3B-2comprises, upon expiration of the resource mode counter 60, the wirelessterminal transmitting (via terminal transmitter circuitry 44) thedevice-to-device (D2D) signals (e.g., to wireless terminal 26 ₂) usingthe resources selected by the wireless terminal from the pre-configureddevice-to-device (D2D) radio resources rather than using thenetwork-allocated radio resources scheduled by the node.

Thus, if the resource mode counter 60 expires, the wireless terminalowning the resource mode counter 60 is explicitly declared to beout-of-coverage, e.g., out-of-coverage of device-to-device (D2D)frequencies. When being declared out-of-coverage, the wireless terminalis permitted to perform out-of-coverage operations, e.g., to use the D2Dradio resource pool 48 for device-to-device (D2D) communications (butnot the device-to-device (D2D) frequencies that are allocated by thenode 22 using scheduling and grants). If the wireless terminal isin-coverage, on the other hand, for device-to-device (D2D)communications the wireless terminal is required to obtaindevice-to-device (D2D) resources/frequencies by scheduling from the node22 (unless, as described below, the node has provided an indication thatwireless terminal may, even when in-coverage, select from thedevice-to-device (D2D) radio resource pool 48). Obtainingdevice-to-device (D2D) resources/frequencies by scheduling from the node22 involves sending a scheduling request to node 22 for device-to-device(D2D) resources, and receiving a scheduling grant from the node 22 inreturn.

The resource mode counter 60 may be realized as any effective way orapparatus of determining a lapse of time since the wireless terminal wasnotified by RRC state machine 52 of any one of the set of predefined RRCIdle state transitions. In an example non-limiting implementation,resource mode counter 60 comprises a clock which counts elapsing timeunits. For example, resource mode counter 60 may be a count-down timerwhich has an initial value set and then is decremented by the passage ofunits of time (e.g., seconds). In a situation in which the time initialvalue is same for each transition of the predetermined set, an exampletime value may be 10 seconds (see, e.g.,http://lteworld.org/forums/lteworld-forum/lte-cell-search, search“period”). In other implementations the resource mode counter 60 maytake other forms, such as a circuit or logic configured to countoccurrences of detection of a network event or marker. For example,resource mode counter 60 may count or track system frame numbers (SFN).

Thus, an initialization (e.g., “initial”) or reference threshold valueof resource mode counter 60 may be configurable. The initializationvalue may be, for example, an integer multiple of wireless terminal cellsearch periods. A “wireless terminal cell search period” is understoodby the person skilled in the art to be a time window allotted for awireless terminal to search for a cell, such as may occur when thewireless terminal is powered on, for example. Alternatively, theinitialization or reference threshold for counter may be multipleattempts of wireless terminal cell search. As yet another alternativeimplementation, the initialization value of the resource mode countermay be set differently for a first of the predefined RRC Idle statetransitions than for a second of the predefined RRC Idle statetransitions. For example, the timer threshold of resource mode counter60 for transition from Camped Normally state to Any Cell Selection Statecan be set higher than the one with transition from Camped on Any Cellstate to Any Cell Selection State.

In the example methods of FIG. 3A and FIG. 3B, preferably the resourcemode counter 60 is started on condition that the resource mode counter60 is not already running and is not already expired. It may be that,under certain circumstances, the resource mode counter 60 is started asa result of a first state transition that appears to indicateout-of-coverage, and following that first state transition a secondstate transition which also appears to indicate out-of-coverage occurs.In such scenario, detection of the second state transition should not“reset” or “restart” the resource mode counter 60, since the cumulativecount after the both the first state transition and the second statetransition should be taken into consideration regarding the timing ofwhen an actual out-of-coverage occurs. In such scenario, the terminalprocessor 40 continues operation of the resource mode counter 60 whenthe wireless terminal undergoes any one of the set of the predefined RRCIdle state transitions and the resource mode counter is already running.

In an example embodiment and mode the method further comprises at leasttemporarily stopping the counter if any one of the following occurs: (1)the wireless terminal finds a suitable/acceptable cell to camp on indevice-to-device (D2D) supported frequencies; (2) the wireless terminalis no longer participating in device-to-device (D2D)services/communications; (3) the wireless terminal determines that thewireless terminal is out-of-coverage; (4) the wireless terminaldetermines to use resource(s) selected by the wireless terminal from apre-configured resource; or (5) the wireless terminal leaves the IdleMode. In comparison with the wireless terminal determining that it isout-of-coverage, the situation in which the wireless terminal determinesto use resource(s) selected by the wireless terminal from apre-configured resource means that the wireless terminal does not have atransitional procedure of determining it is out-of-coverage when thetimer expires, and the wireless terminal may start transmitting D2Dsignals directly.

D. Hardware Implementations

FIG. 4 shows in more detail an example embodiment of the radiocommunications network of any and all of the example embodiments andmodes of FIG. 1A-FIG. 1C. It should be appreciated that FIG. 4 is justone example implementation of how the node 22 and first wirelessterminal 26 ₁ may be carried out structurally and/or functionally. Theexample embodiments an modes of FIG. 1A-FIG. 1C are preferablyimplemented using electronic machinery. The node 22 comprises nodeelectronic machinery 66; first wireless terminal 26 ₁ comprises terminalelectronic machinery 68. In FIG. 1A-FIG. 1C various units andfunctionalities as framed by broken lines of node 22 and first wirelessterminal 26 ₁ are implemented by node electronic machinery 66 andterminal electronic machinery 68, respectively. What comprises node“electronic machinery” is discussed in more detail with reference toFIG. 5.

In the example embodiment of FIG. 4 the node 22 comprises node processor30, also known as a frame processor, and node transmitter 32. The nodetransmitter 32 typically includes plural antenna 32A. The node processor30 is shown in more detail as comprising node scheduler 70 and nodeframe handler 72. In essence, the node scheduler 70 prepares or formats,into frames, information to be transmitted by node transmitter 32 on thedownlink (DL) from node 22 to first wireless terminal 26 ₁ (as well asto other wireless terminals). The node frame handler 72 serves, e.g., toprocess information received in frames on the uplink from wirelessterminals, e.g., first wireless terminal 26 ₁.

The first wireless terminal 26 ₁ comprises terminal processor 40 andterminal transceiver 42. The terminal transceiver 42 typically includesplural antenna 42A. The terminal processor 40 of first wireless terminal26 ₁ of FIG. 4, also known as a frame processor, comprises terminalscheduler 80 and terminal frame handler 82. The terminal frame handler82 analyzes a downlink (DL) portion of a frame as received over radiointerface 24 from node 22. The terminal scheduler 80 prepares uplinkframe for transmission to node 22 or, in the case of device-to-device(D2D) communications, to other wireless terminals such as wirelessterminal 26 ₂.

The first wireless terminal 26 ₁ also comprises executable applications84 and one or more user interfaces (GUIs) 86. The user interfaces (GUIs)86 may be used to operate or interact with one or more of the executableapplications 84. One or more of the applications 84, when executed, mayprompt or involve device-to-device (D2D) communications with anotherwireless terminal, e.g., second wireless terminal 26 ₂. Whendevice-to-device (D2D) communications are invoked or initiated by anapplication, terminal D2D controller 50 superintends or controls thedevice-to-device (D2D) communications.

It was mentioned above that certain units and functionalities of node 22framed by broken line are, in an example embodiment, implemented by nodeelectronic machinery 66. Similarly, certain units and functionalities offirst wireless terminal 26 ₁ framed by broken line are, in an exampleembodiment, implemented by terminal electronic machinery 68. FIG. 5shows an example of such electronic machinery, whether node electronicmachinery 66 or terminal electronic machinery 68, as comprising one ormore processors 90, program instruction memory 92; other memory 94(e.g., RAM, cache, etc.); input/output interfaces 96; peripheralinterfaces 98; support circuits 99; and busses 100 for communicationbetween the aforementioned units.

The memory 94, or computer-readable medium, may be one or more ofreadily available memory such as random access memory (RAM), read onlymemory (ROM), floppy disk, hard disk, flash memory or any other form ofdigital storage, local or remote, and is preferably of non-volatilenature. The support circuits 99 are coupled to the processors 90 forsupporting the processor in a conventional manner. These circuitsinclude cache, power supplies, clock circuits, input/output circuitryand subsystems, and the like.

The resource mode counter 60 may be realized by any appropriatestructure, such as a timer (e.g., a clock-down timer) or other eventcounter that reasonably accurately detects lapse of time since apredetermined Idle State transition. In an example implementation, atimer which is set at an initial value which is decremented is utilized.Alternatively, a count-up timer which, after a predetermined statetransition is utilized, reaches a maximum time-out value may be used todetermine out-of-coverage.

According to the technology disclosed herein, upon any state transitionto Any Cell Selection State (Camped Normally state to Any Cell SelectionState, Camped on Any Cell state to Any Cell Selection State), thewireless terminal shall start resource mode counter 60. Upon any statetransition to Camped Normally on non-D2D frequencies, the wirelessterminal shall start the resource mode counter 60, if it is not runningor not expired. Upon any state transition to Camped on Any Cell onnon-D2D frequencies, the wireless terminal shall start the resource modecounter 60, if it is not running or not expired. For additional safety(as an optional feature), to provide robustness, it is possible thatupon any state transition to Any Cell Selection State, upon any statetransition to Camped Normally on non-D2D frequencies or upon any statetransition to Camped on Any Cell on non-D2D frequencies, the wirelessterminal may be triggered to restart the counter 60, if the counter 60is running.

The technology disclosed herein provides numerous benefits, includingdetermining out-of-coverage condition on the basis of downlink receivedpower since camping procedures are essentially based on downlinkreceived power. In addition, counters such as resource mode counter 60are easily implemented in current networks such as Long Term Evolution(LTE) networks. Yet further, impacts on both legacy Long Term Evolution(LTE) specifications and current cellular services are minimized.

Although the processes and methods of the disclosed embodiments may bediscussed as being implemented as a software routine, some of the methodsteps that are disclosed therein may be performed in hardware as well asby a processor running software. As such, the embodiments may beimplemented in software as executed upon a computer system, in hardwareas an application specific integrated circuit or other type of hardwareimplementation, or a combination of software and hardware. The softwareroutines of the disclosed embodiments are capable of being executed onany computer operating system, and is capable of being performed usingany CPU architecture.

The functions of the various elements including functional blocks,including but not limited to those labeled or described as “computer”,“processor” or “controller”, may be provided through the use of hardwaresuch as circuit hardware and/or hardware capable of executing softwarein the form of coded instructions stored on computer readable medium.Thus, such functions and illustrated functional blocks are to beunderstood as being either hardware-implemented and/orcomputer-implemented, and thus machine-implemented.

In terms of hardware implementation, the functional blocks may includeor encompass, without limitation, digital signal processor (DSP)hardware, reduced instruction set processor, hardware (e.g., digital oranalog) circuitry including but not limited to application specificintegrated circuit(s) [ASIC], and/or field programmable gate array(s)(FPGA(s)), and (where appropriate) state machines capable of performingsuch functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer and processor and controller may be employedinterchangeably herein. When provided by a computer or processor orcontroller, the functions may be provided by a single dedicated computeror processor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, useof the term “processor” or “controller” shall also be construed to referto other hardware capable of performing such functions and/or executingsoftware, such as the example hardware recited above.

Nodes that communicate using the air interface also have suitable radiocommunications circuitry. Moreover, the technology can additionally beconsidered to be embodied entirely within any form of computer-readablememory, such as solid-state memory, magnetic disk, or optical diskcontaining an appropriate set of computer instructions that would causea processor to carry out the techniques described herein.

Some the terminology employed for concepts as described herein has beenupdated or changed in more recent industry documentation, such as the3GPP Technical Standards, for example. As mentioned above,“device-to-device (D2D)” is now also called “sidelink direct”. Someother terminology has also changed, a partial listing appearing in Table1 below.

TABLE 1 Terminology Previous Terminology New Terminology Scheduleassignment SA SCI (Sidelink Control Information) on PSCCH (PhysicalSidelink Control Channel) PD2DSCH (Phys. D2D PSBCH (Phys. SidelinkBroadcast Synch. Channel) Channel) D2DSS SLSS (Sidelink SynchronizationSignals) (D2D synchronization signals) D2D Communications or PSSCH(Physical Sidelink Shared Data Channel Channel) D2D Discovery ChannelDSDCH

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the technology disclosedherein but as merely providing illustrations of some of the presentlypreferred embodiments of the technology disclosed herein. Thus the scopeof the technology disclosed herein should be determined by the appendedclaims and their legal equivalents. Therefore, it will be appreciatedthat the scope of the technology disclosed herein fully encompassesother embodiments which may become obvious to those skilled in the art,and that the scope of the technology disclosed herein is accordingly tobe limited by nothing other than the appended claims, in which referenceto an element in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structural,chemical, and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the technology disclosed herein, for it to beencompassed by the present claims. Furthermore, no element, component,or method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.”

What is claimed is:
 1. A method carried out by a wireless terminal whichis in wireless communications with a radio access node over a radiointerface, the method comprising: performing a cellselection/reselection operation; and setting one frequency to a highestpriority frequency with respect to the cell selection/reselectionoperation while the wireless terminal is simultaneously performing: (i)device-to-device (D2D) communications in a state where the wirelessterminal camps on the one frequency; and (ii) the cellselection/reselection operation.
 2. The method of claim 1, furthercomprising as a result of the selection/reselection operation thewireless terminal selecting a candidate frequency for use in thedevice-to-device (D2D) communications.
 3. The method of claim 1, furthercomprising during the cell selection/reselection operation, requiringthe wireless terminal to set selection/reselection candidate frequenciesat which the wireless terminal cannot receive or transmitdevice-to-device (D2D) signals to be of low priority candidatefrequencies when the wireless terminal is capable of device-to-device(D2D) communications and is receiving or transmitting, or anticipatingreceiving or transmitting, device-to-device (D2D) signals ondevice-to-device (D2D) supported frequencies.
 4. The method of claim 1,further comprising during the cell selection/reselection operation,requiring the wireless terminal to set only cell selection/reselectioncandidate frequencies which are device-to-device (D2D)-supportedfrequencies when the wireless terminal is capable of device-to-device(D2D) communications and is receiving or transmitting, or anticipatingreceiving or transmitting, the device-to-device (D2D) signals on thedevice-to-device (D2D) supported frequencies.
 5. The method of claim 1,further comprising: determining whether the wireless terminal whenengaged in device-to-device (D2D) communications encounters a wirelessterminal selected resource mode; and the wireless terminal determiningwhether to transmit the device-to-device (D2D) signals using resourcesselected by the wireless terminal from pre-configured device-to-device(D2D) radio resources or using network-allocated radio resourcesscheduled by the radio access node based on determining whether thewireless terminal encounters the wireless terminal selected resourcemode.
 6. The method of claim 1, further comprising the wireless terminaltransmitting device-to-device (D2D) signals using device-to-device (D2D)radio resources selected in accordance with the cellselection/reselection operation.
 7. A wireless terminal of acommunications network which communicates over a radio interface with aradio access node, the wireless terminal comprising: a processor; amemory in electronic communication with the processor; instructionsstored in the memory, the instructions being executable to: perform acell selection/reselection operation; and set one frequency to a highestpriority frequency with respect to the cell selection/reselectionoperation while the wireless terminal is simulataneously performing: (i)the device-to-device (D2D) communications in a state where the wirelessterminal camps on the one frequency; and (ii) the cellselection/reselection operation.
 8. The wireless terminal of claim 7,wherein, as a result of the selection/reselection operation, theinstructions are executable to further select a candidate frequency foruse in the device-to-device (D2D) communications.
 9. The wirelessterminal of claim 7, wherein the instructions are executable to furtherrequire, during the cell selection/reselection operation, the wirelessterminal to set selection/reselection candidate frequencies at which thewireless terminal cannot receive or transmit device-to-device (D2D)signals to be of low priority candidate frequencies when the wirelessterminal is capable of device-to-device (D2D) communications and isreceiving or transmitting, or anticipating receiving or transmitting,device-to-device (D2D) signals on device-to-device (D2D) supportedfrequencies.
 10. The wireless terminal of claim 7, wherein theinstructions are executable to further require, during the cellselection/reselection operation, the wireless terminal to set only cellselection/reselection candidate frequencies which are device-to-device(D2D)-supported frequencies when the wireless terminal is capable ofdevice-to-device (D2D) communications and is receiving or transmitting,or anticipating receiving or transmitting, device-to-device (D2D)signals on device-to-device (D2D) supported frequencies.
 11. Thewireless terminal of claim 7, wherein the wireless terminal furthercomprises a transceiver which transmits device-to-device (D2D) signalsusing device-to-device (D2D) radio resources selected in accordance withthe cell selection/reselection operation.